The present invention relates to a process for purifying waste waters using a novel flocculating agent.
Processes for purifying waste waters using dispersions of water-soluble cationic polymers are already known. U.S. Pat. No. 3,409,547 describes, in particular, a process for purifying water using 0.1 to 10 ppm of a quaternary ammonium polymer such as that derived from dimethylaminoethyl methacrylate. European Patent No. 068,955 describes water-in-oil dispersions, which are stable for more than 4 months at 20.degree.-25.degree. C., comprising:
from 20% to 55% of a polymer based on quaternized dimethylaminoethyl acrylate, in the pure form or as a mixture with acrylamide, PA1 from 20% to 45% of at least one C.sub.10 -C.sub.13 normal alkane, PA1 from 1% to 5% of a system comprising at least two emulsifying agents, one of which has a HLB (hydrophilic-lipophilic balance) of 3 to 5 and the other has a HLB of 12 to 16, and PA1 water to make up to 100%. PA1 thermodynamically stability for a period of 30 months or more, PA1 optically transparency, PA1 has Newtonian rheological characteristics up to volume fractions of dispersed phase (sum of the polymer swollen with water and of the surfactant) reaching about 55%, PA1 has a limiting viscosity at a shear gradient of zero (determined at 25.degree. C.) of between about 3 and 500 centipoises, according to the volume fraction of the dispersed phase. PA1 either between 11 and 15 approximately when the water-soluble cationic vinyl monomer is either by itself or as a mixture with a water-soluble anionic vinyl monomer, PA1 or between 7.5 and 13 approximately when the water-soluble cationic vinyl monomer is in a mixture with a water-soluble non-ionic vinyl monomer. PA1 from 25 to 65 parts by weight of the aqueous solution (A), PA1 from 25 to 60 parts by weight of the oily phase (B), and PA1 from 10 to 27 parts by weight of the non-ionic surfactant (C). PA1 R.sub.1 is a linear or branched alkyl radical having from PA1 R.sub.2 is a linear or branched alkyl radical having from 2 to 4 carbon atoms, PA1 R.sub.3, R.sub.4 and R.sub.5, which may be identical or different, are linear or branched alkyl radicals or aryl radicals, and PA1 X is chosen from halogen atoms and the groups --C.sub.2 H.sub.5 --SO.sub.4 and --CH.sub.3 --SO.sub.4. PA1 polymerization of the water-soluble cationic vinyl monomer on its own or as a mixture with a comonomer, PA1 if the cationic monomer is mixed with a comonomer, the nature (anionic or non-ionic) and proportion of the latter, PA1 the nature of the cationic monomer, and PA1 the nature of the oily phase (B). PA1 photochemical polymerization conditions, for example by ultraviolet irradiation, and/or PA1 thermal polymerization conditions, by bringing the microemulsion into the presence of a hydrophobic free-radical initiator (such as azo-bisisobutyronitrile) introduced with the oily phase (B) or a hydrophilic free-radical initiator (such as potassium persulphate or ammonium persulphate) introduced with the aqueous solution (A), or into the presence of a redox system in which the persulphate is used in combination with at least one reducing agent chosen from the polyhydrophenols, sodium sulphite and odium bisulphite, dimethylaminopropionitrile, the diazomercaptans and the ferricyanides.
These dispersions, which are suitable as flocculating agents for the clarification of waste waters, consist of particles generally between 200 and 2,000 nm in of and having a size polydispersity at least equal to 2.
U.S. Pat. No. 4,588,508 describes a mixture, used for the clarification of water, of two cationic polymers having a bimodal molecular weight distribution. British Patent No. 2,178,432 describes the use, for the flocculation of solids in suspension in water, of 1 to 10,000 ppm, relative to the said solids, of a mixture of a strongly cationic polymer and at least one weakly cationic polymer. The obvious drawback of the solutions proposed in these two latter documents lies in the complexity resulting from the preliminary formation of two different polymers.